Thread forming screw

ABSTRACT

A thread forming screws including opposite flanks connecting the screw crest region with the screw root region and tapering outwardly toward the root region, with each flank being formed of outer and inner flank sections tapering toward the root sections at different angles, and with the crest region being formed of a first region section ( 8 ) extending parallel to a central axis of the screw and a second, inclination region section ( 7 ) inclined toward the root region ( 5 ) in a direction opposite a setting direction (S) at an angle of from about 10° to about 45°.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a thread forming screw to be setin a hard component such as concrete and having a stem, and a threadprofile provided on at least a portion of a longitudinal extent of thestem and formed as a trapezoidal thread having a crest region, a rootregion, and two flanks connecting opposite ends of the crest region withthe root region and tapering outwardly toward the root region, with eachflank being formed of outer and inner flank sections with a flank angleformed by the outer flank sections being smaller than a flank angleformed by the inner flank sections.

[0003] 2. Description of the Prior Art

[0004] Screws of the type described above serve for securing objects onhard constructional components such as, e.g., concrete. To this end, abore is formed in the constructional component in which the screw isset. Upon being screwed into the bore, the thread profile provided onthe screw stem cuts or rolls a thread in the wall of the bore. Becauseof the hardness and brittleness of the constructional component, thethread profile of the screw should have a specific shape.

[0005] A screw of the type discussed above is disclosed in GermanUtility Model DE-U1-93 02 186. The trapezoidal thread of the screw has aroot region, a crest region that defines the outer diameter of the screwthread, and flanks that connect the crest region with the root regionand are formed of outer and inner flank sections forming different flankangles toward the root region, with the outer flank sections forming anangle of 30° and the inner flank section forming an angle of 60°. Byforming the inner flank sections with a greater flank angle than theouter flank sections, advantageously, the thread is reinforced in theroot region due to the increase of the material thickness in thisregion. In particular for hard constructional components, providing athread with a reinforced root region increases substantially theload-carrying capability of the screw disclosed in DE-01-93 02 186.

[0006] However, because of the high friction between the bore wall andthe crest region of the thread, the screw does not have adequatescrew-in characteristics.

[0007] Moreover, the manufacturing of this screw is rather expensive asseveral steps are required in order to provide the screw with thedesired thread profile.

[0008] Accordingly, an object of the present invention is to provide athread forming screw having adequate screw-in characteristics.

[0009] Another object of the present invention is to provide a threadforming screw that can be economically produced.

SUMMARY OF THE INVENTION

[0010] These and other objects of the present invention, which willbecome apparent hereinafter, are achieved by forming the crest region ofa first region section extending parallel to a central axis of the screwand a second, inclination region section inclined toward the root regionin the direction opposite the setting direction at an angle from about10° to about 45°.

[0011] The provision of the inclination region section in the crestregion permits to improve the flow characteristics of a material, e.g.,steel which is used for forming the screw. The improved flowcharacteristic permits, in turn to obtain a precise geometry of thethread and, as a result, optimal screw-in characteristics. On the otherhand, providing an inclined flank section permits to obtain, during thesetting of the inventive screw into the constructional component, aso-called “snow plow effect” which consists in that the material, whichis comminuted by the outer crest region, is carried away by theinclination section, and is compressed by an excess material thicknesssection resulting from the increased flank angle formed by the innerflank sections. The first region section of the crest region functionsas a chisel, removing the wall material.

[0012] To insure optimal cutting off, comminuting, and carrying away thewall material, advantageously the extent of the crest region in thesetting direction corresponds to about 1-4 times of the extent of theinclination region section in this direction. Dependent on the screwdimensions and operational characteristics, the extent of the region cancorrespond (coinside) substantially with the extent of the inclinationregion section.

[0013] Advantageously, the root region has a two-sided recess forming aroot angle of about 150°-170°. This angle proved to be optimal to insurethat sufficient material is available for formation of the thread.Otherwise, an excess accumulation of the comminuted material in therecess would take place, preventing the increase of friction between thescrew and the wall of the bore upon the screw being screwed-in.

[0014] In an advantageous embodiment of the inventive screw, anequal-sided recess is formed. This permits to precisely define, duringthe manufacturing of the inventive screw, the yield limit.

[0015] To obtain optimal screw-in characteristics, the thread profile isadvantageously formed as a double thread, with the two-section flanksbeing provided on the first, in the setting direction, thread, with theouter flank sections forming a flank angle of from about 30° to about50° and the inner flank sections forming a flank angle from about 60° toabout 90°.

[0016] For manufacturing reasons, the second thread is formed withflanks having a flank angle of from about 60° to about 90°.

[0017] In order to obtain, during setting of the inventive screw, anoptimal ratio between the material carrying-away step and thecompression step of the comminuted material, the thread is so formedthat the maximum outer diameter of the first thread preferablycorresponds to 1.1÷1.3 times of the maximum outer diameter of the secondthread.

[0018] Further, preferably, the break point between first and secondflank section is so selected that its diameter corresponds approximatelyto 1.2 times of the core diameter of the screw.

[0019] The novel features of the present invention, which are consideredas characteristic for the invention, are set forth in the appendedclaims. The invention itself, however, both as to its construction andits mode of operation, together with additional advantages and objectsthereof, will be best understood from the following detailed descriptionof preferred embodiments, when read with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Single FIGURE of the drawings shows a cross-sectional profile ofa thread forming screw according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] A thread forming screw according to the present invention, inparticular a concrete screw, a cross-sectional profile of which is shownin the drawing, has a stem 1 provided with a tip (not shown) facing in asetting direction S and with a thread profile 3. The thread profile 3 isformed as a trapezoidal thread. A crest region 4, which defines an outerdiameter d1, is connected with a root region 5, by outwardly taperingtoward the root region 5, flanks 6. The thread can be formed as a doublethread, as shown in the drawing, or as a single thread. For the sake ofclarity, the drawing shows only one side of the thread profile 3 and thecentral axis M of the inventive screw.

[0022] The crest region 4 has a first region section 8, which extendsparallel to the central axis M, and a second inclination region section7 which is inclined toward the root region at an angle δ, e.g., of 15°.The inclination region section 7 adjoins the parallel to the centralaxis region section 8 at the end of the region section 8 facing in adirection opposite the setting direction S. When the thread profile 3 isformed as a double thread, the crest region 10 of the second thread 12does not have an inclination region.

[0023] The flanks 6 of the first thread 11 have two different flankangles a and β, with the outer flank angle α being smaller than theinner flank angle β. The outer flank angle α can be equal, e.g., 40° andthe inner flank angle β can be equal, e.g., 75°. The flank angle γ ofthe second thread 12 can be equal, e.g., also 75°.

[0024] The root region 5 has an equal-sided recess 9 with a root angle εof, e.g., 162°.

[0025] The maximum outer diameter dl of the first thread 11 corresponds,e.g., to 1.24 times of the maximum outer diameter d4 of the secondthread 12. Further, the diameter d3 of the break point 13 of the firstthread 11 corresponds, e.g., to 1.2 times of the core diameter d2 of thescrew.

[0026] The extent of the crest region 4 of the first thread 11 in thesetting direction S corresponds to the extent C of the crest region 10of the second thread 12. The extent a, in the setting direction of thecrest region 4 of the first thread 11 corresponds to a double of theextent b of the inclination region section 7 in the setting direction.

[0027] Though the present invention was shown and described withreferences to the preferred embodiment, such are merely illustrative ofthe present invention and are not to be construed as a limitationthereof, and various modifications to the present invention will beapparent to those skilled in the art. It is, therefore, not intendedthat the present invention be limited to the disclosed embodiment ordetails thereof, and the present invention includes all of variationsand/or alternative embodiments with in the spirit and scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. A thread forming screw for setting in a hardconstructional component, comprising a stem (1); and a thread profile(3) provided on at least a portion of a longitudinal extent of the stemand formed as a trapezoidal thread having a crest region (4), a rootregion (5), and two flanks (6) connecting opposite ends of the crestregion (4) with the root region (5) and tapering outwardly toward theroot region (5), each flank being formed of outer and inner flanksections with a flank angle formed by the outer flank sections ofopposite flanks (6) being smaller than a flank angle formed by innerflank sections, and the crest region (4) being formed of a first regionsection (8) extending parallel to a central axis of the screw and asecond, inclination region section (7) inclined toward the root region(5) in a direction opposite a setting direction (s) at an angle (δ) offrom about 10° to about 45°.
 2. A screw according to claim 1, wherein anextend (a) of the crest region (4) in the setting direction (s)corresponds to about 1÷4 times of an extend (b) of the second,inclination region section (7) in the setting direction.
 3. A screwaccording to claim 1, wherein the root region (5) has a two-sided recess(9) forming a root angle (,) from about 150° to about 170°.
 4. A screwaccording to claim 3, wherein the recess (9) is formed as an equal-sidedrecess.
 5. A screw according to claim 1, wherein the trapezoidal threadis formed as a double thread, and wherein the two-section flanks areprovided on a first, in the setting direction, thread (11).
 6. A screwaccording to claim 1, wherein the first flank angle (∀) amounts to fromabout 30° to about 50°, and the second flank angle (∃) amounts to fromabout 60° to 90°.
 7. A screw according to claim 5, wherein the secondthread (12) has straight flanks.
 8. A screw according to claim 7,wherein the flanks of the second thread form an angle (γ) from about 60°to 90°.
 9. A screw according to claim 5, wherein a maximum outerdiameter (dl) of the first thread (11) corresponds to 1.1÷1.3 times of amaximum outer diameter (d4) of the second thread (12).
 10. A screwaccording to claim 1, wherein a diameter (d3) of a break point (13)formed by two flank sections corresponds approximately to 1.2 times of acore diameter (d2) of the screw.